1. Field of the Invention
The present invention generally relates to a semiconductor structure, and more particularly to a method for growing a group-III nitride semiconductor heteroepitaxial structure on a silicon substrate.
2. Description of the Prior Art
The semiconductor light-emitting diode (LED) structure comprises a substrate, a light emitting structure, and a pair of electrode for powering the diode. The substrate can be an opaque or a transparent substrate. The Light emitting diodes are based on gallium nitride compounds which generally comprise: a transparent and insulating substrate, e.g., a sapphire substrate. In general, to overcome the substantial lattice mismatch between the insulating substrate, e.g., a sapphire substrate, and GaN compound semiconductor, it is a common practice to provide a thin buffer layer or a nucleation layer on the insulating substrate, which is formed followed by a layer on which an LED structure is grown. The growth of single crystals on the insulating substrates that has been studied for many years. Early works included the growth of both silicon and III–V compound semiconductors on a variety of insulating substrates that including sapphire. In these studies, it was determined the usage of nucleation or buffer layers is to reduce the occurrence of imperfections and the tendency towards twinning in the thicker layer grown thereon.
Group-III nitride semiconductors [GaN (gallium nitride), InN (indium nitride), AlN (aluminum nitride), and their alloys] have become the materials of choice for many optoelectronic applications, especially in the areas of fully-color or white light-emitting diodes (LEDs) and blue laser diodes (LDs). Some scientists and engineers have even predicated that group-III nitride semiconductors will become all-around semiconductors besides their already-commercialized applications in optoelectronics. At present, the major barrier for widespread applications of nitrides is lack of perfectly lattice-matched substrates for epitaxial growth. Sapphire (Al2O3) and silicon carbide (SiC) are two most popular materials as the substrates. Beside the large lattice mismatch, the insulation property of sapphire renders the processing of nitride devices more difficult and costly. On the other hand, the high price and limited size of silicon carbide also make the widespread GaN-on-SiC applications difficult. GaN-on-Si epitaxial technology represents an interesting alternative, which can eventually integrate the existing Si-based microelectronic technology and the novel functionalities provided by the group-III nitrides.
For GaN-on-Si heteroepitaxy, the AlN single-layered buffer can provide good results as reported in the literature, and leading to the demonstration of light-emitting diodes on Si. However, the mutual solubility of Al and Si is very high at the AlN buffer-layer growth temperature (about 820° C. vs. eutectic temperature 577° C.). Therefore, the inter-diffusion of Al and Si at the interface is severe, resulting in high unintentional doping levels in the epilayer and the Si substrate as well as the degradation in the film structural and optical quality.
On the other hand, it has been found that an amorphous or polycrystalline SiNx [silicon nitride (Si3N4) or silicon subnitride] layer can be formed by intentional or unintentional nitridation of the silicon substrate surface during the first stage of the group-III nitride growth. Moreover, Si3N4 is well known to be an effective diffusion barrier material. However, this amorphous or polycrystalline SiNx layer is prone to cause detrimental effects on the properties of GaN films grown on the Si substrate, since it is not possible to grow a high-quality crystalline film on an amorphous or polycrystalline surface. Therefore, it has been a common practice in the growth of group-III-nitrides film on the silicon substrate to avoid the formation of an amorphous or polycrystalline SiNx layer during the first stage of the group-III nitride growth. To overcome the effects of amorphous or polycrystalline SiNx on the growth quality and to facilitate an effective diffusion barrier layer the formation of a single-crystal diffusion baffler layer which can be lattice matched to the Si(111) surface is highly desirable.